package com.xtwy.utils;

/**
 * @描述：
 *
 * 分布式ID生成工具
 *
 * @公司：  山西迅腾伟业
 * @版本：  1.0.0
 * @日期：  18/08/02
 * @作者：  侯建军
 */
public class SnowFlakeUtil {
    private final static int DATA_CENTER_ID=1;
    private final static  int MACHINE_ID=1;
    /**
     * 起始的时间戳
     */
    private final static long START_STMP = 1480166465631L;

    /**
     * 每一部分占用的位数
     */
    private final static long SEQUENCE_BIT   = 12;    // 序列号占用的位数
    private final static long MACHINE_BIT    = 5;     // 机器标识占用的位数
    private final static long DATACENTER_BIT = 5;     // 数据中心占用的位数

    /**
     * 每一部分的最大值
     */
    private final static long MAX_DATACENTER_NUM = -1L ^ (-1L << DATACENTER_BIT);
    private final static long MAX_MACHINE_NUM    = -1L ^ (-1L << MACHINE_BIT);
    private final static long MAX_SEQUENCE       = -1L ^ (-1L << SEQUENCE_BIT);

    /**
     * 每一部分向左的位移
     */
    private final static long    MACHINE_LEFT    = SEQUENCE_BIT;
    private final static long    DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
    private final static long    TIMESTMP_LEFT   = DATACENTER_LEFT + DATACENTER_BIT;
    private static SnowFlakeUtil instance;
    private long                 sequence = 0L;     // 序列号
    private long                 lastStmp = -1L;    // 上一次时间戳
    private long                 datacenterId;      // 数据中心
    private long                 machineId;         // 机器标识

    private SnowFlakeUtil(long datacenterId, long machineId) {
        if ((datacenterId > MAX_DATACENTER_NUM) || (datacenterId < 0)) {
            throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
        }

        if ((machineId > MAX_MACHINE_NUM) || (machineId < 0)) {
            throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
        }

        this.datacenterId = datacenterId;
        this.machineId    = machineId;
    }

    public static void main(String[] args) {

        // 2为数据中心号,3为机器ID
        SnowFlakeUtil snowFlake = new SnowFlakeUtil(2, 3);
        long          start     = System.currentTimeMillis();

        for (int i = 0; i < 1000000; i++) {
            System.out.println(snowFlake.nextId());
        }

        System.out.println(System.currentTimeMillis() - start);
    }

    /**
     * 产生下一个ID
     *
     * @return
     */
    public synchronized long nextId() {
        long currStmp = getNewstmp();

        if (currStmp < lastStmp) {
            throw new RuntimeException("Clock moved backwards.  Refusing to generate id");
        }

        if (currStmp == lastStmp) {

            // 相同毫秒内，序列号自增
            sequence = (sequence + 1) & MAX_SEQUENCE;

            // 同一毫秒的序列数已经达到最大
            if (sequence == 0L) {
                currStmp = getNextMill();
            }
        } else {

            // 不同毫秒内，序列号置为0
            sequence = 0L;
        }

        lastStmp = currStmp;

        return (currStmp - START_STMP) << TIMESTMP_LEFT    // 时间戳部分
               | datacenterId << DATACENTER_LEFT           // 数据中心部分
               | machineId << MACHINE_LEFT                 // 机器标识部分
               | sequence;                                 // 序列号部分
    }

    /**
     *
     * @Title: getInstance
     * @Description:更改服务器，请在base模块中修改常机器ID
     * @author 侯建军
     * @date 2018年7月27日 下午2:17:08
     * @version V1.0
     * @param @return    参数
     * @return SnowFlakeUtil    返回类型
     */
    public static synchronized SnowFlakeUtil getInstance() {
        if (instance == null) {
            instance = new SnowFlakeUtil(DATA_CENTER_ID, MACHINE_ID);
        }
        return instance;
    }
    private long getNewstmp() {
        return System.currentTimeMillis();
    }
    private long getNextMill() {
        long mill = getNewstmp();

        while (mill <= lastStmp) {
            mill = getNewstmp();
        }
        return mill;
    }
}

